Genetics Exam 1 Study Guide

What is difference between prokaryotic and eukaryotic cell?

Prokaryotic vs. Eukaryotic Cells

∙ Prokaryotic Cells:

o Unicellular

o Cell wall/plasma membrane

o No nucleus but does have ribosomes and DNA, DNA is not highly  organized

o Ex: archaebacteria and eubacteria

o Chromosomes can be replicated rapidly and then the cell divides o Rate of reproduction depends on amount of resources

∙ Eukaryotic Cells:

o Membrane bound organelles

o Genetic material is held in nuclear envelope and forms nucleus o Plant Cell

 Cell Wall

 Chloroplast

 Vacuole

o Animal Cell

 Plasma membrane

∙ Chloroplasts and mitochondria have their own chromosomes DNA

∙ X chromosome structure is formed by 2 sister chromatids, this is not  always the structure that DNA takes

∙ Chromatids= 1 strand of DNA wrapped around proteins in a coiled  structure

What causes genetic variation?

∙ Homologous Pairs= Copies/pairs of chromosomes  

∙ Heterozygous=same gene with different alleles(Aa)

∙ Homozygous= same gene with same alleles(AA)

∙ In humans p is the short arm and q is the long arm in chromosomes ∙ Loci on homologous pairs of the same

∙ If chromosomes are fairly similar, the chromosomes will line up o If differing info/chromosome w/ extra information then a loop will  be created

∙ Sister chromatids are made during genetic replication

o Heterozygous and homozygous do not happen in sister  chromatids

∙ Submetacentric= means sister chromatids are almost attached in the  middle

∙ Metacentric=sister chromatids are attached directly in the middle ∙ Telocentric= sister chromatids are attached at the top Don't forget about the age old question of epsilon n proof of convergence

∙ Acrocentric=sister chromatids are attached almost at the top ∙ Diploid=2 sets of genetic material(can go through  

How is an individual's sex determined genetically?

meiosis),chromosomes have a homologous pair

∙ Haploid= 1 set of genetic info(can’t do meiosis)

∙ Cohesion= protein that holds chromatids together, key to behavior of  chromosomes in mitosis and meiosis, at anaphase cohesion breaks  down so sister chromatids can separate, at anaphase 1 cohesion on  chromosomes breaks down but centromere is protected by  shugoshin(protein)

∙ Allele= 2 different genes at the same locus

∙ Some chromosomes develop fragile sites that are prone to breakage  and can be associated with specific sequences and phenotypic  abnormalities  

Viruses

∙ Have DNA or RNA

∙ Neither prokaryotic or eukaryotic

∙ Have outer protein coat surrounding nucleic acid

Mitosis vs. Meiosis*(be able to haploid and diploid cells in different stages of  mitosis and meiosis)*

∙ Mitosis:

o Happens in haploid and diploid organisms

o In humans, Chromosomes 1-22 are somatic and 23 are sex  chromosomes

o Cell Cycle:  

 G1

 G1/S Checkpoint: monitor if cell is ready to on next step  S: synthesis(where 2nd chromatid comes from)

 G2:Growth and metabolism

 G2/M Checkpoint: monitor if ready to divide or go through  mitosis

 M(mitosis): separation of sister chromatids

 Spindle assembly checkpoint

 Cytokinesis: dividing of cytoplasm

o G1-G2 is interphase where the cell metabalises and grows  o Mitosis contains prophase, prometaphase, metaphase, anaphase, telophase Don't forget about the age old question of act 353 class notes
We also discuss several other topics like ge4+ electron configuration
If you want to learn more check out math 2414 utd

o Prophase=create 2 chromatid structure

o Prometaphase= chromosomes move towards center of cell o Metaphase=chromosomes line up on metaphase plate We also discuss several other topics like kamasutra monkey pulls the turnip

o Anaphase= separation of sister chromatids

o Telophase=chromatids are separated to both cells and cell  membrane begins to form

o Interphase  Mitosis, Nuclear envelope breaks down

o Mitosis produces two genetically identical diploid cells  

∙ Meiosis:

o Production of haploid gametes

o Fertilization= the fusion of haploid gametes(egg+sperm)

o Genetic variation is the consequence of meiosis

o 2n cell goes through meiosis to make 1n spores, spores go  through mitosis to make gametes

o HAPLOID cells CANNOT go through meiosis b/c it cannot divide  cellular DNA in half

o Steps:

 Interphase: DNA synthesizes and chromosome replication  phase

 Meiosis 1: separation of homologous chromosome pairs  and reduction of the chromosome # by ½

 Meiosis 2: separation of sister chromatids, also known as  equal division, 1n(Very similar to mitosis!)

o Metaphase 1 homologous pairs align along metaphase plate o Produces 4 cells from 1 cell

o Each new cell is haploid

o Newly formed cells from meiosis are genetically different from  each other, depends on how chromosomes align on metaphase  plate

Genetic Variation

∙ Crossing over= where chromatids overlap one another and swap DNA  ∙ Mutants

o Complementation= determine whether mutants are at the same  lous or at different loci

o Mutants in more than one gene can cause a similar phenotype ∙ Duplications and deletions  If you want to learn more check out 2170003

o Duplication= addition of genes

o Deletion=omittance of genes

 Large deletions are easily detected and during pairing the  normal chromosome will loop out

o Can be caused by unequal crossing over

o Missing gene copies can cause unbalanced expression and lead  to a certain phenotype

o Haplo insufficiency= One copy of certain genes is NOT sufficient  for normal development

∙ Inversion

o The flipping of genes along a chromosome

o Pericentric inversion= involve centromere, info not gained or lost in inversion

o Paracentric inversion=only occurs at one end

 Homologs struggle to find each other

 For them to pair up, they will form an inversion loop to  match up the loci

o Meiosis

 Homozygous: no problems arise

 Heterozygous: homologs sequences align only if the 2  

chromosomes form an inversion loop, demonstrate  

reduced recombination in an inversion, as gametes form  

result in nonviable offspring

 Double crossing over avoids centromere problems

∙ Translocation

o Occurs in nonhomologous chromosomes

o Special mitotic arrangements occur to accomadate  

translocations  

o Nonreciprocal translocation= a piece of 1 chromosome gets  stuck on another chromosome and chromosome 1 is missing  information

o Reciprocal translocation= exchange information(chromosome 1  and chromosome 2 switch information)

o Robersonian translocation=damage on 2 chromosomes near end, 2 chromosomes join together and metacentric chromosome is  kept but fragment chromosome is lost

Formation of gametes in Males and Females

∙ Spermatogenesis and oogenesis occurs in animals

∙ Males(spermatogenesis)

o Start with 2n spermatogonium cell

o Primary spermatocyte 2n

o Meiosis 1

o Secondary spermatocyte 1n

o Meiosis 2

o Spermatids that mature into sperm

o Takes about 48 hours

∙ Females(oogenesis)

o Oogonium 2n

o Primary oocyte

o Meiosis 1(happens in embryo)

o Secondary oocyte (1n) & first polar body(secondary oocyte goes  through meiosis 2)

o Second polar body & ovum 1n

o Can take 50 years

Mendel & Genetics

∙ Used experimental approach and analyzed results mathematically ∙ Studied easily differentiated characteristics with only 2 possibilities for  each characteristic

∙ Monohybrid cross= cross b/w 2 parents that differ in a SINGLE  characteristic

∙ Mandel controlled fertilization and would take pollen from one parent  and put it in the stoma of the other parent

∙ Traits of parents do not blend

∙ Limitations of crosses: if have nondiscrete phenotypes and/or  multigenetic traitscant be analyzed w/ this approach

∙ Mendel’s 1st law: (principle of segregation) each individual diploid  organism possesses 2 alleles for any particular characteristic. These 2  alleles segregate when gametes are formed and one allele goes into  each gamete

∙ Dominance= when 2 different alleles are present in a genotype, only  the trait encode by one of them. The dominant allele is observed in the phenotype

o If phenotype is dominant, cannot tell if homozygous or  heterozygous and need to use a test cross(Aa x aa)

o Punnent square is used in a test cross

∙ Dihybrid crosses= examine 2 unrelated traits at the same time ∙ Segregation=separation of homologous chromosomes  ∙ Independent assortment= different genes are on different  chromosomes and are independent of each other

∙ Multiplication rule= want to determine likelihood of 2 different events  occurring at the same time

o Ex: dice rolling, a 4 twice in a row 1/6 x 1/6 =1/36

o Ex: R(1/2) x R(1/2)=1/4

∙ Addition rule= Two ways to get the same outcome

o Ex: Dice rolling a 3 or a 4 1/6 +1/6=1/3

o Ex: Rr(1/4) x Rr(1/4)= heterozygous (1/2)

∙ Dihybrid crosses: think about it like doing two monohybrid crosses at  once

o 9:3:3:1 ratio  

o (Figure 3.10)

∙ Chi-Square Goodness of Fit= indicates the probability that the  difference between the observed and expected values is due to chance o H0= the null hypothesis, any observed difference is due to  chance(there is no “real” difference b/w observed and expected o Have to look at critical values table and find the degrees of  freedom on the side of the table and then find 0.05 point across  the top of the table.

 If the values are to the left of 0.05 you fail to reject the null hypothesis

 If the values are to the right of 0.05 then you reject the null hypothesis

o Chi squared= Σ[(observed-expected)2 / expected]

∙ Pedigree= pictoral representation of a family history, a family tree that  outlines the inheritance of one or more characteristics (need to know  how to read a pedigree)

o Can look at inheritance w/o doing a pure genetic cross o Helpful with disease inheritance

o If male and females are equally effected then it is an autosomal  trait

o If every infected person has an infected parent and NO carriers  then the trait is dominant

o Autosomal recessive traits will have equal frequency in males  and females and it often skips a generation  

∙ Proband= the person from whom the pedigree is initiated for ∙ Gene interaction= effects of genes at one locus depends on the  presence of genes at other loci

Sex

∙ Sex is determined by different mechanisms in different species ∙ Sexual reproduction: alternates b/w haploid and diploid states ∙ Homogametic: same sex chromosome  

∙ Heterogametic: different sex chromosomes

∙ Most organisms have 2 sexual phenotypes male and female ∙ Sexual phenotypes: males have sperm and females have eggs o If female and male don’t have eggs and sperm then they are  referred to as something else

∙ In humans, X&Y chromosomes pair during meiosis even though they  are not truly homologous

o The Y chromosome determines sex and not much else

o XX/XY system is used in mammals

∙ XX/XO system

o XX female

o XO male

∙ ZZ/ZW system

o ZZ male

o ZW female

o Used in birds, snakes, butterflies, some amphibians and fish o May not look the same in all species, but the MALES are  homogametic

∙ Genetic Sex-Determining System

o No sex chromosomes, sex-determining genes on autosomes  Found in some fish, plants, fungi, protozoans

o Environmental factors

 Temperature

 Where positioned w/in group of embryos

∙ SRY gene on Y chromosome determines maleness(only found in males o Turner syndrome: XO, 1/3000 female births

o Kleinefelter syndrome: XXY or XXXY or XXXXY or XXYY, 1/1000  male births  

o Poly-X females: 1/1000 female births

∙ Barbodies

o In female cells, the inactivated X chromosome

o When gametes are made , X chromosomes are activated, when  gametes come together in theory one should shut off but doesn’t actually happen(think of patchy cat)

o Lyon= how sometimes maternal and sometimes paternal X is  active

o Epigenetic silencing= methyl groups that change chromatin  organization

∙ Y-linked characteristics: only found in males

o All male offspring will exhibit that trait

o Y chromosome has lost DNA over time

o Important for sex determination in SRY

∙ Sex-influenced and sex-limited characteristics

o Sex-influenced= one sex has a more severe phenotype  Ex: adams apple

o Sex-limited= one sex exhibits trait

Dominance

∙ Complete dominance= one gene is completely dominant and the other is not being expressed

∙ Incomplete dominance=have different intermediates (range) of  phenotypes and one trait is not clearly dominant  

o Ex: red flower x white flower = color range from light pink to red ∙ Codominance= can have one of two alleles or both and whichever are  present will show

o Ex: L1L1= will have L1 phenotype, L2L2= will have L2  

phenotype, L1L2= will have both phenotypes

∙ Penetrance= the percent of individuals having a particular genotype  that express the expected phenotype (individual)

∙ Expressivity= the degree to which a character is expressed(how severe the characteristic is expressed in individuals)

∙ Psuedodominance= expression of a normally recessive mutation that is produced when the dominant wild-type allele in a heterozygous  individual is absent due to a deletion on one chromosome

o This individual is essentially hemizygous for a recessive trait ∙

Lethal Alleles

∙ Lethality occurs at somepoint in development, missing part in  population is a clue to fatal allele

Multiple Alleles

∙ For a given locus, more than 2 alleles are present w/in a group of  individuals

∙ Think ABO blood types, only 2 alleles but 3 options

Epistasis

∙ One gene masks the effect of another gene

∙ Recessive: recessive allele of one gene masks the phenotype for a  second gene

∙ Duplicate recessive epistasis: have to have at least one dominant allele for each of 2 genes to see phenotype

Variations in copy #

∙ Aneuploidy= +1 or more or -1 or more  

o Deletion of centromere during mitosis and meiosis  

o Nondisjunction during mitosis and meiosis

o All other diploid sets are functioning normally but one is not o Effects:

 Humans: sex-chromosome aneuploids(turner syndrome,  Kleinfelter syndrome) autosomal: Trisomy 21(down  

syndrome)

∙ Primary down syndrome, 75% random nondisjunction

in egg formation

∙ Familial Down syndrome, Robertsonian translocation  

b/w chromosomes 14 & 21

∙ Frequency of aneuploidy changes with increasing  

maternal age

 Plants: mutants could actually be trisomics, survive more  often

∙ Polyploidy

o Autopolyploidy: single species, entire genome mistake,  nondisjunction cytokinesis doesn’t occur (same species)

o Allopolyploidy: 2 different species mate, frequent in plants  (mules) (different species)

 Allotriploid: combination of 2 species and a triploid so a 3n  individual. 2n+n=3n

o Significance: increased cell size, larger plant attributes,  evolutionmay give rise to new species

∙ Nullisomy= losss of both members of a homologous pair of  chromosomes. (2n-2)

∙ Monosomy=loss of a single chromosome(2n-1)

∙ Trisomy= gain of a single chromosome(2n+1)

o Trisomy 21: three 21 chromosomes  

∙ Tetrasomy=gain of 2 homologous chromosomes (2n+2) ∙ Nondisjunction(mitosis)= happening at the level of sister chromatids  splitting

o As that cell continues to divide the clones continue to have that  issue